Flexible ring interconnection system

ABSTRACT

Multiple small conductive and flexible hollow rings, each of which is made from a pliable material, provide a flexible connection medium for use between a substrate and a microelectronic device package. Each ring is soldered to both the substrate and the device. A portion of the sidewall of each ring is not soldered thus insuring that at least part of the ring stays flexible. The rings accommodate elevation differences on a substrate and electronic device package. They also provide a vibration resistant and flexible joint.

REFERENCE TO RELATED APPLICATIONS

This application claims priority from United States provisional patentapplication Nos. 60/575,347 and 60/575,348, both of which were filed May28, 2004.

BACKGROUND OF THE INVENTION

The present invention relates generally to high-density electricalinterconnections structures and more particularly to such aninterconnection structure that may be used in interposer applicationsand to connect electrical devices to circuit boards.

Microelectronic devices such as state-of-the-art microprocessors requirelarge numbers of reliable connections in increasingly-small areas. Asthe number of connections between an electronic device and a substrateto which the device is to be mounted increases, the likelihood that justa single connections will not be made or will fail increases.

In “wave soldering,” an electronic components is soldered to a substrateby flowing molten solder over a substrate in which electronic componentsare mounted. A substrate, to which electronic components are to besoldered, is passed over the flowing, molten solder such that exposedmetal and fluxed surfaces on the lower surface of the substrate surfacewick the molten solder upward from the solder bath. As the substratewith the wicked, molten solder moves away from the molten solder bath,the solder cools and solidifies, establishing an electrical connectionbetween electronic devices and soldered surfaces of the substrate.

As connection density increases in the electronic arts and lead lengthsfrom electronic devices decreases, the increasing number of connectionsthat must be made make it statistically more likely that even a singleconnection will not be made or will fail. Even minor irregularities in asubstrate's planarity can cause connection problems.

One problem with prior art soldering techniques arises when the contactsurfaces of a substrate and an electronic device are separated from eachother by different distances. For example, if one or two contact leadsor one or two contact surfaces of a microprocessor are more widelyseparated from a planar substrate than the other contact leads orcontact surfaces, the molten solder might not wick between the substrateand the more-distant contact surfaces of the electronic device. Priorart soldering techniques suffer from an inability to make a connectionwhen the spacing or distance between contact surfaces of two devices orsurfaces to be joined, varies by more than a small amount.

When even a single connection between an electronic device and itssupporting substrate is either not made at the time of manufacture, orfails while in use, the cost to identify a failed electrical connectionand to repair it can often exceed the cost to manufacture the product inwhich the electronic device and supporting substrate operates. Improvingthe manufacturability of electrical connections and improving thereliability of electrical connections after manufacture would be animprovement over the prior art.

The present invention is directed to a connector structure that issuitable for use in high-destiny applications, is easy to manufactureand which provides a reliable contact force while avoiding theaforementioned shortcomings.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a connectordevice that has a plurality of flexible, conductive rings arranged in anarray so as to contact conductive pads on a circuit board and contactsor contact pads of an opposing electronic device.

Microelectronic devices are electrically connected and mounted to acircuit board or other planar surface using small conductive hollowrings between electrical contacts of an electronic device and a circuitboard or substrate. Each ring is a band of pliant conductive materialthat extends around a center point. An axis of rotation extends througheach ring. Each ring's axis of rotation is substantially parallel to theother axes or rotation and to the plane of the substrate and the planeof the electronic device.

Each ring acts as a small, round spring-type of contact which willdeform when a force is directed toward the interior of the ring from anydirection. When the force is removed, the ring will return to itsoriginal shape. The resilient behavior of the rings provide a small,flexible interconnection which can accommodate variations in theplanarity of opposing surfaces. Each ring's flexibility alsoaccommodates circuit board or substrate flexing as well as impacts andvibration.

These and other objects, features and advantages of the presentinvention will be clearly understood through a consideration of thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of this detailed description, the reference will befrequently made to the attached drawings in which:

FIG. 1 is a perspective view of a discrete conductive hollow ringconstructed in accordance with the principles of the present invention,and which is suitable for connecting an electric device to a circuitboard or other substrate;

FIG. 1A shows the deformation of the discrete conductive hollow ring ofFIG. 1 in response to an externally-applied force;

FIG. 2 is a side elevation of a microelectronic device and a pluralityof conductive hollow mounting rings mounted to a substrate;

FIG. 3 is a side elevation of a conductive mounting ring filled with aresilient, non-conductive material and the ring being soldered to asubstrate;

FIG. 4 is a side elevation of a substrate and a plurality of conductivehollow mounting rings mounted to an electronic device; and,

FIG. 5 shows a conductive ring and the space between an electronicdevice and a substrate filled with non-conductive resilient material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of a discrete conductive hollow ring 10which is constructed in accordance with the principles of the presentinvention and which may be used for the mounting of an electronic deviceto a circuit board or other substrate. In the embodiment shown, theconductive hollow ring 10 has a diameter D substantially the same as thelength L of the ring 10, but other configurations may be used.

The ring is preferably made up of a band of pliant conductive material,such as a copper or gold alloy or a spring steel coated or plated with agood conductor such as copper or gold. Alternate embodiments can includeresilient plastics that are either plated or otherwise conductivelycoated. Regardless of its material, as is true of all rings, thematerial from which it is made is centered about a point in space 12through which extends an axis of rotation 14 for the ring 10. A force,F, exerted on the ring 10 from the exterior, and directed radiallyinward of the ring, will cause the ring 10 to deflect as shown in FIG.1A. As is well-known, as the force F increases past the material'selastic limit, the ring will collapse but as long as the applied force Fremains below the elastic limit of the ring material, the ring 10 willact as a spring, and return to its original shape when the applied forceis removed. The spring-like action of the ring 10, when used as in arrayof rings will provide a connection that can accommodate planaritydifferences between a substrate 8 and an electronic device 6. It canalso provide a connection that can be flexed and which will be moretolerant of impact and vibration. The improved physical robustness isprovided by the flexible material from which the ring 10 is made, aportion of which between the substrate 8 and device 4 is not soldered.The rings may be easily by electro forming or electro-dischargemachining to maintain the tolerances down to critical sizes anddiameters, such as 500 micrometers and the like.

The ring 10 illustrated is provided with two strips, or bands, ofnickel-plating 20, 22 that run along the side of the ring 10 from oneopen end to the other. The nickel plating bands 20 and 22 act as and arereferred to herein as solder barriers 20 and 22. As shown, they aresubstantially opposite to each other on the exterior surface of the ring10. They prevent solder from wicking all the way up and around thecircumference of the ring, thereby insuring that at least part offlexible ring side wall will not be soldered to the substrate 8 or anopposing surface, but rather will still remain pliant.

As shown in FIG. 3, when the ring 10 is attached to a substrate 8,molten solder will only wick upwardly until it reaches the solderbarriers 20 and 22. Solder that wicks upward along the exterior of thering 10 will form fillets 24 between the ring's 10 lower curvature (FIG.10) and the top of the substrate 8 as part of the normal solderingprocess. The solder barriers 20 and 22 insure that flexible materialfrom which the ring 10 is made will not be completely coated with solderduring a soldering process, insuring that the ring 10 will retainflexibility.

In a preferred embodiment as shown in FIG. 1, the ring 10 side wallcross-section is substantially planar or rectangular. In an alternateembodiment, the ring side wall cross-section can be circular, oval orother shape although non-rectangular side wall shapes might tend to bemore rigid. Inasmuch as a circle and an oval are both special caseellipses, the more general side wall shape is referred to herein aselliptical.

FIG. 2 is a side elevation of a microelectronic device 4 positioned justabove a plurality of conductive hollow mounting rings 10, the assemblyof which comprise a connector 2 for mounting the electronic device 4 toa circuit board or other substantially planar substrate 8. Each of therings 10 in FIG. 2 is substantially the same as the ring 10 shown inFIG. 1 albeit in FIG. 2, the solder barriers 20 and 22 are not visible.

The mounting rings 10 in FIG. 2 are aligned to that each of their axes14 are parallel to each other and extending into the plane of thefigure. In an alternate embodiment, the rings 10 can have their axesco-linear.

Inasmuch as the axes 14 extend into the plane of FIG. 2, the axes 14 ofthe rings 10 also tend to extend parallel to the plane of the substrate8 which also extends into the plane of FIG. 2, as well as the plane ofthe underside 6 of the device 4. The side walls of each ring therefore“face” the substrate 8 and the underside 6 of the device 4. The planesin which the ring 10 open ends lie are substantially orthogonal to thesubstrate surface 8 and the underside 6 of the electronic device 4.

The several discrete conductive hollow rings 10 each provide a redundantsignal path along its body between conductive traces on the surface 8 ofthe substrate and connection points or nodes on the under side 6 of theelectronic device 4. Signals can traverse both sides of the ring to getfrom circuits on the device 4 to circuits on the substrate 8 below. Thisdual signal path also assist in reducing the inductance of the system inwhich such contacts are used. As shown in FIG. 2, the several conductiverings 10 are initially attached to the substrate 8 and provide aconnector for the device 4.

FIG. 3 shows an alternate embodiment of a conductive ring 10 wherein theinterior 18 of the ring 10 is filled with a resilient, non-conductivematerial 18, such as silicone. The aforementioned solder fillets 24mechanically and electrically attached the ring 10 to the substrate 8.Filling the interior 18 space with a resilient material increases thestrength of the ring 10 but also prevents solder from flowing into theinterior space 18 by either wicking or capillary action.

FIG. 4 shows a connector 2 for mounting an electronic device. In FIG. 4,the connector 2 is formed using the aforementioned discrete conductiverings 10, but the connector 2 in FIG. 4 includes a non-conductive underfill material 26 which holds the conductive rings 10 in place withrespect to each other. The under fill material 26 can be anon-conductive silicone layer, the thickness of which is less than theoutside diameter of the conductive rings 10. When the electronic device4 is urged downward, each of the rings will deform slightly. Becausethey are pliable, with each of them tending to oppose a downwardcompressive force, each conductive ring 10 will tend to make physicalcontact with the surface of the substrate 8 below it as well as thesurface 6 of the electronic device 4 above it. Each ring will thereforeprovide a better electrical and physical contact than is otherwisepossible with a straight pin used in the prior art.

FIG. 5 shows a non-conductive, resilient under fill material 26 disposedbetween the device 4 and a substrate. It also shows the hollowconductive ring 10 filled with the under fill material, adding stiffnessto the ring 10.

The connector 2 shown in FIG. 4 can be initially attached to thesubstrate 8 or to the electronic device 4. It can be wave soldered toeither the substrate 8, the device 4 or both of them simultaneously.

As shown in FIG. 2 and FIG. 3, each of the hollow contact rings 10 ofthe connector 2 shown in FIG. 4 has solder barriers (not shown in FIG.4) which prevent molten solder from wicking all the way around the ring10 thereby defeating the flexibility provided by the thin metal fromwhich the rings are made.

The hollow, conductive rings are preferably made from electronicallyconductive metals that will also accept a solder barrier. Copper, silverand gold are excellent conductors and can be alloyed with other metalsthat can provide good resilience; they can also be locally plated withsolder-barrier metals such as nickel. The rings 10 can also be formedfrom metal-plated plastics.

Those of skill in the art will appreciate that since each of the rings10 can be slightly compressed from its original shape that the rings canovercome slight variations in the planarity of the substrate 8 and/orthe electronic device 4. By providing a solder barrier that preventssolder from wicking all the way around a ring, each ring's flexible sidewalls acts as a small round spring and will deform when a force isdirected toward the interior of the ring. When the force is removed, thering will return to its original shape. The resilient behavior of therings provide a small, flexible interconnection which can accommodatevariations in the planarity of opposing surfaces. Each ring'sflexibility also accommodates circuit board or substrate flexing as wellas impacts and vibration. The resulting connection between the substrate8 and an electronic device 4 is more tolerant of substrate and/or deviceflexing. The connection is also less susceptible to shock orvibration-induced failure.

While the preferred embodiment of the invention have been shown anddescribed, it will be apparent to those skilled in the art that changesand modifications may be made therein without departing from the spiritof the invention, the scope of which is defined by the appended claims.

1. A connector for mounting a microelectronic device having a planarmounting surface to a planar substrate, the connector comprising: aplurality of discrete conductive hollow rings, each ring being a band ofpliant conductive material around a corresponding center point for eachring, and through which extends an axis of rotation for each ring, theband of pliant material enclosing a hollow volume, the axes of rotationof the rings being parallel to each other, parallel to the plane of thesubstrate and the plane of the connector.
 2. The connector of claim 1,wherein each ring includes a rectangular cross-section.
 3. The connectorof claim 1, wherein each ring includes an elliptical cross-section. 4.The connector of claim 1, wherein the hollow volume of each said ring isfilled with a resilient, non-conductive material.
 5. The connector ofclaim 1, wherein each of said rings is provided with first and secondsolder barriers disposed on exterior surfaces of said ring.
 6. Theconnector of claim 5, wherein said solder barriers are disposed oppositeeach other on the circumferences of said rings, the first and secondsolder barriers inhibiting the wicking of molten solder around theentire circumference of a ring.
 7. A substrate for mounting amicroelectronic device, comprising: a planar substrate supportingconductive traces that are capable of carrying electrical signals; aplurality of discrete conductive hollow rings, each of the rings beingelectrically coupled to at least one conductive trace on the substrate,each said rings including a band of pliant conductive material extendingaround a corresponding center point for each said ring, and throughwhich extends an axis of rotation for each said ring, the band of pliantmaterial enclosing a hollow volume, said rings being arranged so thataxes of rotation of said rings are disposed parallel to the plane ofsaid substrate, said rings being located on said planar substrate in apattern so as to mate with contact surfaces of an electronic component.8. The substrate of claim 7, wherein each ring is provided with firstand second solder barriers on the surface of each ring that are locatedopposite each other on the circumference of each ring, the first andsecond solder barriers inhibiting the wicking of molten solder aroundthe entire circumference of a ring.
 9. An electronic device comprising:a planar connection surface having a plurality of electrical signalcontact surfaces; an electrically conductive hollow contact ring that iselectrically connected to each electrical contact surface, each ringbeing a band of pliant conductive material around a corresponding centerpoint for each ring, and through which extends an axis of rotation foreach ring, the band of pliant material enclosing a hollow volume, theaxes of rotation of the rings being parallel to each other and parallelto the planar connection surface, the plurality of discrete conductivehollow rings being located on the planar connection surface to mate withcontact surfaces of a planar substrate.
 10. The electronic device ofclaim 9, wherein each ring is provided with first and second solderbarriers on the surface of each ring that are located opposite eachother on the circumference of each ring, the first and second solderbarriers inhibiting the wicking of molten solder around the entirecircumference of a ring.
 11. A spring contact for use connectingelectrical circuits of two members together, comprising: a ring having acontinuous body of conductive material, the ring having an internalhollow volume and an exterior surface that defines a circumference ofthe ring body, said ring body having two opposing top and bottomsurfaces interconnected together by two intervening side surfaces, aportion of each of said side surfaces including a solder-resistantmaterial disposed thereon.
 12. The spring contact of claim 11, whereinsaid hollow volume is filled with a non-conductive material.
 13. Thespring contact of claim 12, wherein said non-conductive materialincludes silicone.